This invention relates generally to electrostatic discharge grounding switches and their method of operation, and more particularly to an electrostatic discharge switch mounted on a card assembly and coactable with the mounting frame to automatically discharge any electrostatic charge on the ground plane of the card as the card is inserted into the mounting frame. Near completion of insertion the switch is moved to an open position so that the card ground plane is insulated from the frame by the time the card is fully inserted.
In printed circuit board technology and especially in the technology involved in computers often a multiplicity of circuit cards and/or boards are utilized in the machine. It is usually required to provide the printed circuit card with a ground plane as a part of its structure and which ground plane is maintained at a signal ground potential which is different from the electrical potential of the mounting frame which is commonly called the machine ground potential. Thus, the ground plane of the cards have a signal ground different from the machine ground, and hence the card signal ground planes are insulated from the machine ground plane.
One of the problems encountered with printed circuit cards is that the signal ground planes tend to build up an electrostatic charge. Since this ground plane is maintained at a level different from that of the mounting frame and is insulated therefrom, when the card is inserted into the mounting frame the electrostatic discharge will not automatically be discharged to machine ground but may remain thereon. This can be especially harmful if the card is inserted into the connectors on the card while the machine is in operation.
There have been many prior art proposals for grounding of various cards, components, boards, cartridges and the like. For example U.S. Pat. No. 4,179,178 teaches a technique for grounding of the contacts on a game cartridge being inserted into a computer during insertion of the card, and thereafter offering the ground. This does not teach the grounding of a signal ground to a machine ground temporarily during card insertion and the patent which backs various schemes of grounding include U.S. Pat. Nos. 4,439,809; 4,456,800; and 4,510,553.